Numerous methods are known for the production of fatty acid amide by the reaction of corresponding fatty acid, anhydride or lower alkyl esters thereof with ammonia. These reactions can be accomplished with or without catalyst at elevated temperature and at very high pressure as described in U.S. Pat. No. 3,253,006 but the trend has been to use processes which do not require the use of high pressure and still provide high conversion with high selectivity to the desired amide product. Accordingly, catalytic procedures have been developed whereby the reaction of the fatty acids with ammonia can be achieved by substantially reduced pressures and, in some cases, even at atmospheric pressure.
U.S. Pat. No. 2,013,108 describes a process of atmospheric amidation reaction, which involved passing through gaseous ammonia into the fatty acid melts that contained a surface catalyst, which was a solid inorganic substance. The major drawback -for such process is that it typically requires very long reaction time that may be 48 or more hours to achieve acceptable levels of conversion and consequently some of the amide is dehydrated to the corresponding nitrile.
One of the competing reactions in amidation of carboxylic acids to amide is the dehydration of amide to nitrile, and this is promoted by long reaction time, therefore short reaction time is preferred in order to achieve higher yield of amide. Processes requiring shorter reaction time and employing reaction condition, which minimise undesirable by-product formation, have been developed. According to U.S. Pat. No. 3,816,483, the amidation process can be conducted at atmospheric pressure coupled with shorter time of reaction (11 hours); the formation of nitrile by-product is reduced. The catalysts used in this process are from the Group IVb or Vb metal, preferably a compound of titanium, zirconium or tantalum.
Furthermore, in U.S. Pat. No. 4,277,410, the same approach of amidation reaction is used but the catalyst employed is more specifically to alkyltin catalyst in an amount of 0.25% to 4% by weight. Other than that, U.S. Pat. No. 4,655,972 discloses the use of catalytic amount of hydrated oxide, preferably hydrated titanium, zirconium and tin oxide in an amount of 0.05% to 10% by weight. This process requires high. temperature which is in the range of 120° C. to 240° C. and pressure which is in the range of 100 kPa to 1000 kPa to achieve a good yield.
In view of starting materials for the synthesis of fatty acid amide, most commonly used raw material is the fatty acid itself, but British Patent No. GB 939378 discloses the use of long carbon chain fatty esters (C12 to C30) as the feed stock and reacting it with gaseous ammonia under high pressure and temperature. Non patent literature (Cravatt et al) revealed the use of acid halide typically the one with chlorine atom, which is more reactive compare to fatty acid and esters when react with ammonia.
On the other hand, most of the prior art use gaseous ammonia as starting material to react with the fatty moiety to give the desired amide. in Cravatt et al, urea and thiourea (Beckwith) are used instead of ammonia to react with fatty moiety to yield the fatty acid amide. Other than that, the U.S. Pat. No. 2,070,991 discloses the use of liquid ammonia instead of gaseous ammonia for the amidation process.
In general, it can be said that the usual methods have at least one of three serious drawbacks. Either the methods require long reaction time of at least 11 hours as disclosed in U.S. Pat. Nos. 4,277,410 and 4,655,972, or the methods need to be carried out at high temperature and pressure (e.g. 240° C. and 136 atm) as disclosed in U.S. Pat. No. 3,253,006, or the methods require the synthesis of an expensive intermediate compound as found in non patent literature.
Accordingly, it is an object of this invention to provide such a method of synthesis for normal amide of fatty acids. It is a further object of this invention to provide such a method of synthesis that will give high percentage yield of amide with a short reaction time. It is a still further object of this invention to provide such a method of synthesis that does not require the use of expensive intermediate compounds. It is another object of this invention to provide such a method of synthesis that does not require high pressure to give high percentage yield of fatty amide.